Marilyn Monroe Would be Interested

[Recusant]

I like to think so, anyway. 

An article describing a new paper about the composition of diamonds. The authors of the paper say there is evidence that the carbon in diamonds originating from over 300 km (186 miles) deep is at least partially organic in origin. The sparkling stones are made up of stuff that was once alive, in other words. I didn't know that there was such a thing as "oceanic diamonds," which also feature in the paper.

"Some Rare Diamonds Form Out of The Remains of Once-Living Creatures, New Study Finds" | Science Alert

Despite humanity's intense fascination with sparkly pieces of carbon, it seems there is still plenty to learn about how diamonds form deep within our planet.

New research has discovered that two different types of rare diamonds share a common origin story – the recycling of once-living organisms over 400 kilometers (250 miles) below the surface.

There are three main types of natural diamonds. The first are lithospheric diamonds, which form in the lithospheric layer around 150 to 250 kilometers (93 - 155 miles) below the surface of Earth. These are by far the most common, and probably the type of diamond you'd find on an engagement ring.

Then there are two rarer types - oceanic and super-deep continental diamonds.

Oceanic diamonds are found in oceanic rocks, while deep continental diamonds are those formed between 300 and 1,000 kilometers (186 and 621 miles) below the surface of Earth.

Just to put that in perspective, we categorize space as 100 kilometers (62 miles) above sea level, the ISS orbits about 400 km (250 miles) above Earth, and humans have never managed to dig deeper than 12.2 km (7.6 miles) into the ground. So, super-deep continental diamonds form... super deep in Earth's mantle.

As you would expect, oceanic and super-deep continental diamonds seem pretty different. Because variation in a carbon isotope signature called δ13C (delta carbon thirteen) can be used to determine whether the carbon has an organic or inorganic origin, past researchers have suggested that oceanic diamonds originally formed from organic carbon that was once within living beings.

Super-deep continental diamonds, on the other hand, have an extremely variable amount of δ13C. It's hard to tell whether they're made of organic carbon or not.

But in this new paper, led by Curtin University geologist Luc Doucet, the team found that the cores of super-deep continental diamonds have a similar δ13C composition. Surprisingly, this means that, like oceanic diamonds, these gems also contain the remains of once-living creatures.

[Continues . . .]

The paper is open access.

"Oceanic and super-deep continental diamonds share a transition zone origin and mantle plume transportation" | Nature - Scientific Reports

Abstract:

Rare oceanic diamonds are believed to have a mantle transition zone origin like super-deep continental diamonds. However, oceanic diamonds have a homogeneous and organic-like light carbon isotope signature (δ13C − 28 to − 20‰) instead of the extremely variable organic to lithospheric mantle signature of super-deep continental diamonds (δ13C − 25‰ to + 3.5‰).

Here, we show that with rare exceptions, oceanic diamonds and the isotopically lighter cores of super-deep continental diamonds share a common organic δ13C composition reflecting carbon brought down to the transition zone by subduction, whereas the rims of such super-deep continental diamonds have the same δ13C as peridotitic diamonds from the lithospheric mantle. Like lithospheric continental diamonds, almost all the known occurrences of oceanic diamonds are linked to plume-induced large igneous provinces or ocean islands, suggesting a common connection to mantle plumes.

We argue that mantle plumes bring the transition zone diamonds to shallower levels, where only those emplaced at the base of the continental lithosphere might grow rims with lithospheric mantle carbon isotope signatures.

[¶ added. - R]

[Recusant]

If I were to start noting the sociological outrages and questionable imagery it could take a  few paragraphs. The chandeliers are memorable. 

Tribal dances of the Nacirema tribe:

[Tank]

I missed this first time around. Very interesting.

[hermes2015]

The actors all looked old then.